Power converter

ABSTRACT

A power converter connected between a direct current power supply and a load, the power converter including a switching unit energizing the load based on inputted control signal, a voltage detector detecting a voltage of the direct current power supply, and a protection operation portion detecting a steep elevation of the voltage and performing protection operation to stop a switching operation by the switching unit, wherein the protection operation portion includes an addition circuit adding a predetermined voltage to the voltage detected by the voltage detector and a delay time generator connected to an output of the addition circuit, and wherein the protection operation is performed when a difference between the voltage detected by the voltage detector and an output voltage of the delay time generator reaches a certain value.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation to an International Application No.PCT/JP2016/077658, filed on Sep. 20, 2016 which is based upon and claimsthe benefit of priority from Japanese Patent Application No.2015-193655, filed on, Sep. 30, 2015, the entire contents of which areincorporated herein by reference.

FIELD

Embodiments of the invention disclosed herein relate a power converter.

BACKGROUND

For example, an inverter that drives a three-phase brushless motor or aconverter that converts direct current voltage perform power conversionby connecting a switching unit to a direct current power supply andturning switching elements on and off. A battery such as a lithium ionbattery or a rectified and smoothened commercial alternating powersupply converted into stabilized voltage for example are used as thedirect current power supply.

Such direct current power supply experiences a voltage variation ofapproximately 20% of the reference voltage depending upon thecharging/discharging state of the battery or by variation of commercialalternating current power supply, etc. Thus, in order to protect circuitelements from overvoltage, an overvoltage protection circuit isimplemented to the switching unit. In the overvoltage protectioncircuit, it is widely accepted to employ a configuration in which, forexample, a voltage value of the direct current power supply is comparedwith a threshold value for judging occurrence of overvoltage by using acomparator and a predetermined protection operation is performed whenthe voltage value exceeds the threshold value.

Elements such as a low-pass filter having a cutoff frequency lower thanthe operating frequency of the switching unit is often connected to thecircuit detecting the direct current voltage. This is is because a steepvoltage change does not occur in normal operation and a filter with alarge time constant is connected to deal with noise. Elements such as anisolation amplifier unsuitable for high speed operation are alsoconnected in order to insulate the main circuit from the control circuitin consideration of safety and reliability. Thus, a direct currentvoltage detection circuit generally has poor responsiveness and theovervoltage protection operation may be delayed on the order of severaltens of μs to several hundreds of μs with respect to a high slew ratevoltage change caused by external factors. Thus, in consideration of theresponsiveness of the detection circuit, a configuration to limit theoperation of the switching unit by operating ahead of the protectionthreshold value of the overvoltage protection circuit is proposed asdisclosed in JP 2010-136506 A which is a published Japanese patentapplication.

SUMMARY Problem Solved

However, in the configuration disclosed in the above describedpublication, when the inductance of the reactor connected to the outputside of the switching unit is extremely large, large electric power maybe regenerated to the direct current power supply side at the time ofprotection operation to cause an instantaneous voltage elevation and mayresult in application of voltage exceeding the device rating before theovervoltage protection operation becomes valid. Especially when a powergenerator or the like is connected as the load of the switching unit,excessively large regenerative electric power is produced by magneticenergy. It is thus, not possible to limit the direct current voltagewithin the device rating voltage by merely restricting the operation ofthe switching unit. It is therefore, required to take measures such asincreasing the capacitance of a smoothening capacitor.

Thus, a power converter is provided that possess a high speedovervoltage protection function capable of suppressing the directcurrent voltage within the device rating voltage even when excessivelylarge electric power is regenerated from the output side.

Solution To Problem

A power converter connected between a direct current power supply and aload includes a switching unit energizing the load based on an inputtedcontrol signal, a voltage detector detecting a voltage of the directcurrent power supply, and a protection operation portion detecting asteep elevation of the voltage and performing protection operation tostop a switching operation of the switching unit, wherein the protectionoperation portion includes an addition circuit adding a predeterminedvoltage to the voltage detected by the voltage detector and a delay timegenerator connected to an output of the addition circuit, and whereinthe protection operation is performed when a difference between thevoltage detected by the voltage detector and an output voltage of thedelay time generator reaches a certain value

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 pertains to a first embodiment and illustrates a switching unitand its protection circuit.

FIG. 2 illustrates a specific configuration of the protection circuit.

FIG. 3 is a timing chart illustrating the case in which the protectioncircuit operates in the first embodiment.

FIG. 4 is a timing chart illustrating the case in which the protectioncircuit dues not operate in the first embodiment.

FIG. 5 pertains to a second embodiment and illustrates the switchingunit and its protection circuit.

FIG. 6 pertains to a third embodiment and illustrates the switching unitand its protection circuit.

FIG. 7 is an operation timing chart according to the third embodiment.

FIG. 8 pertains to a fourth embodiment and illustrates the switchingunit and its protection circuit.

FIG. 9 is a chart indicating a voltage elevating speed to which twoprotection circuit portions are capable of responding.

FIG. 10 pertains to a fifth embodiment and illustrates the switchingunit and its protection circuit.

FIG. 11 pertains to the fifth embodiment and illustrates an example of aconfiguration of an overvoltage detection circuit.

FIG. 12 is a timing chart illustrating the case in which the protectioncircuit operates in the fifth embodiment.

FIG. 13 is a timing chart illustrating the case in which the protectioncircuit does not operate in the fifth embodiment.

FIG. 14 pertains to another embodiment and illustrates a comparingmethod of signals.

DESCRIPTION First Embodiment

A description will be given hereinafter on a first embodiment withreference to FIGS. 1 to 4. FIG. 1 illustrates a switching unit and itsprotection circuit. Two ends of a direct current power supply 1 areconnected to power supply lines 3 and 4 via a relay switch 2. Asmoothening capacitor C1 and a voltage detection circuit 5 are connectedbetween the power supply lines 3 and 4. The voltage detection circuit 5corresponds to a voltage detector.

The voltage detection circuit 5 is provided with a voltage dividingcircuit, a differential circuit, and the like, not specifically shown.The voltage detection circuit 5 detects the direct current voltagebetween the power supply lines 3 and 4 and outputs a detection signalVdet to a threshold signal generating circuit 6 and an inverting inputterminal of a comparator CP1. The threshold signal generating circuit 6generates a threshold signal Vth1 based on the inputted detection signalVdet and outputs the threshold signal vth1 to the noninverting inputterminal of the comparator CP1.

The comparator CP1 compares the detection signal Vdet and the thresholdsignal Vth and outputs a low active overvoltage judging signal Vcmp(trigger signal) to a retaining circuit 7. The retaining circuit 7outputs an interruption signal V0V1 that retains the state of change ofthe signal Vcmp. The interruption signal V0V1 is directly inputted to alogic circuit LC1 and is further inputted to a logic circuit LC2 afterbeing transformed to an inverted interruption signal V0V2 through a deadtime generating circuit 8.

A drive control signal is inputted to the logic circuits LC1 and LC2 bya control IC 9. The logic circuits LC1 and LC2 correspond to a logicoperator. The logic circuits LC1 and LC2 output signals obtained bylogically synthesizing the drive control signal and interruption signalsV0V1 and V0V2 to the gates of semiconductor switching elements SW1 andSW2 via gate drivers 10 and 11. The switching elements SW1 and SW2 areIGBTs for example and are series connected between the power supplylines 3 and 4 to constitute a switching unit 12. A load 13 is connectedparallel with the switching element SW2.

As illustrated in FIG. 2, in the threshold signal generating circuit 6,an addition signal Vadd generated by an addition voltage generatingcircuit 14 is given to the noninverting input terminal of an operationalamplifier OP1 via a resistor element R1. The detection signal Vdet isfurther given to the noninverting input terminal via a resistor elementR2. A series circuit of resistor elements R4 and R3 is connected betweenthe output terminal of the operational amplifier OP1 and ground. Acommon connection point of the resistor elements R4 and R3 is connectedto the inverting input terminal of the operational amplifier OP1. Theseelements constitute an addition circuit 15 and the addition circuit 15adds the detection signal Vdet and the addition signal Vadd and outputsthe sum.

A delay time generator 16 formed of a resistor element R5 and acapacitor C2 is connected to the output terminal of the addition circuit15. A delay time based on time constant z is given to the input signal(Vdet+Vadd) by the delay time generator 16. The signal outputted fromthe delay time generator 16 is the threshold signal Vth1. The delay timegenerator 16 corresponds to an integration circuit. The voltagedetection circuit 5, the threshold signal generating circuit 6, thecomparator CP1, the retaining circuit 7, and the logic circuits LC1 andLC2 described above constitute a protection circuit 17. The protectioncircuit 17 corresponds to a protection operation portion.

Next, a description will be given on the operation of the presentembodiment with reference to FIGS. 3 and 4. As illustrated in FIG. 3,the voltage of the threshold signal Vth1 is higher than the voltage ofthe detection signal Vdet by the amount of addition signal Vadd and thechange in the voltage of the threshold signal Vth1 is delayed by timeconstant τ. When overvoltage occurs between the power supply lines 3 and4, difference is created in the magnitudes of voltage elevation of thedetection signal Vdet and the threshold signal Vth1 and thus, thedetection signal Vdet becomes temporarily greater than the thresholdsignal Vth1 (Vdet≥Vth1) (see (a) to (C)). As a result, the comparatorCP1 outputs overvoltage judging signal Vomp and the overvoltage judgingsignal Vcmp is retained as the interruption signal V0V1 by the retainercircuit 7 (see (d)).

The signal retaining circuit 7 is preferably a circuit such as a latchcircuit capable of resetting the retaining state of the signal V0V1 byan external signal inputted by the control IC 9 for example. Byemploying such configuration, it is possible to disable the operation ofthe protection circuit 17 by a reset signal while an electric vehicle isundergoing rapid battery charge for example. Alternatively, a timer maybe activated from the moment the overvoltage judging signal Vomp becomesactive and the retaining state may be reset after lapse of a certaintime for example.

When the interruption signal V0V1 is outputted, the inverted signal V0V2of the signal V0V1 is outputted (see (e)) after the lapse of the delaytime given by the dead time generating circuit 8. The delay timeprovides a dead time in which both the switching elements SW1 and SW2are turned OFF and is approximately several μs for example.

The signals V0V1 and V0V2 interrupt the drive control signals of theswitching elements SW1 and SW2 in the logic circuits LC1 and LC2 andprotect the circuit from overvoltage by fixing the ON/OFF states of theswitching elements SW1 and SW2 to predetermined states. For example, incase of an overvoltage caused by a load dump during regeneration,switching element SW1 in the high pressure side is turned OFF and theswitching element SW2 in the low pressure side is thereafter turned ON(see (f), (g)) to form a short circuit loop with the load 13 and theswitching unit 12 and provide protection by consuming electric power.

That is, the protection circuit 17 of the present embodiment detectsovervoltage at high speed based on the difference in the voltage changerates of the detection signal Vdet and the threshold signal Vth1. Theresponse properties of the protection circuit 17 may be changedarbitrarily by the time constant r and the addition signal Vadd used inthe generation of the threshold signal Vth1. Further, the additionsignal Vadd may be readily modified to voltage dividing resistance ormicrocomputer output and the time constant z may be readily modified toRC time constant depending upon the device being used.

Further, in case the voltage between the power supply lines 3 and 4 doesnot undergo a steep elevation in a magnitude to exceed the devicebreakdown voltage, the protection circuit 17 does not operate since thesize relation of the detection signal Vdet and the threshold signal Vth1is maintained as illustrated in FIG. 4.

According to the present embodiment described above, with respect to theswitching unit 12 that is connected between the direct current powersupply 1 and the load 13 and that energizes the load 13 based on theinputted control signal, the protection circuit 17 detects a steepvoltage elevation of the direct current power supply 1 detected by thevoltage detection circuit 5 and executes a protection operation to stopthe switching operation by the switching unit 12. The protection circuit17 is provided with the addition circuit 1.5 that adds the additionsignal Vadd to the detection signal Vdet and the delay time generator 16connected to the output of the addition circuit 15. The protectioncircuit 17 executes a protection operation when the difference betweenthe detection signal Vdet and the threshold signal Vth1 which is anoutput voltage of the integration circuit and which is given the timeconstant τ reaches a certain value.

According to the above described configuration, it is possible to detecta steep overvoltage without measuring the time using a timer or the likeand thereby allowing the size and cost of the protection circuit 17 tobe reduced compared to conventional protection circuits because theprotection circuit 17 compares the detection signal Vdet and thethreshold signal Vth1 using a comparator CP1, it is possible to rapidlydetect indications leading to overvoltage.

Further, the switching unit 12 is configured by two switching elementsSW1 and SW2 connected parallel to the direct current power supply 1 andthe protection circuit 17 causes the switching unit 12 to short circuitthe load 1 as a protection operation. Thus, in case the load 13 is astator winding of a motor for example, the rotation of the motor may bestopped by short circuit braking.

Further, the protection circuit 17 is provided with logic circuits LC1and LC2 that generate a drive signal for the switching unit 12 byperforming a logical operation of the drive control signal given by thecontrol IC 9 and interruption signals V0V1 and V0V2 which are based onthe overvoltage judging signal Vcmp generated for performing theprotection operation, and the logic circuits LC1 and LC2 execute theprotection operation with priority over the drive control signal. It isthus, possible to rapidly stop the switching operation of the switchingunit 12 when detecting an indication leading to overvoltage.

Second Embodiment

In the following description, elements that are identical to those ofthe first embodiment are identified with identical reference symbols andare not re-described. A description will be given on the differencesfrom the first embodiment. As illustrated in FIG. 5, the dead timegenerating circuit 8 and the logic circuits LC1 and LC2 are removed froma protection circuit 21 of the second embodiment and the interruptionsignal V0V1 outputted by the retaining circuit 7 is inputted to acontrol IC 22 replacing the control IC 9. That is, in the secondembodiment, the control 22 performs the operation indicated in FIG. 3instead of the circuitry it replaces.

When the interruption signal V0V1 is inputted, the control IC 22performs a protection operation as illustrated in FIG. 3 by fixing agate signal VH to low level and thereafter fixing a gate signal VL tohigh level after the lapse of dead time. In the second embodiment,generation of the dead time and the interruption to the drive controlsignal are controlled by the software of the control IC 22 and thus, itis possible to reduce the circuit size though the response speed isreduced.

Third Embodiment

Next, a description will be given on a third embodiment with referenceto FIGS. 6 and 7. A protection circuit 31 of the third embodiment isprovided with a voltage change rate detection circuit 32 configured by adifferentiation circuit for example instead of the threshold signalgenerating circuit 6. A voltage change rate signal Vdiff outputted fromthe voltage change rate detection circuit 32 is given to thenoninverting input terminal of the comparator 181 and a threshold signalVth2 is given to the inverting input terminal of the comparator CP1.

Next, a description will be given on the operation of the thirdembodiment with reference to FIG. 7. When the voltage of the directcurrent power supply 1 elevates suddenly, the voltage change is detectedby the voltage chance rate detection circuit 32 and the level of voltagechange rate signal Vdiff is increased (see (a) and (c)). When thevoltage change rate signal Vdiff exceeds he threshold signal Vth2 (see(b)), the comparator CP1 outputs the overvoltage judging signal Vcmpwhich is retained as an interruption signal V0V3 by the retainingcircuit 7 (see (d)). When the interruption signal V0V3 is outputted, itsinverted signal V0V4 is outputted (see (e)) after the lapse of the delaytime given by the dead time generating circuit 8. The rest of theoperation is the same as the first embodiment. In the third embodiment,the voltage change rate is detected directly by the differentiationcircuit. Thus, protection can be provided at the same time as theoccurrence of overvoltage. However, in devices heavily affected bynoise, surge noise or the like may increase the differentiation value ofthe voltage change and cause the protection circuit 31 to be operated.Thus, the use of the protection circuit 17 of the first embodiment isconsidered to be appropriate especially when the influence of noise islarge.

Fourth Embodiment

Next, a description will be given on a fourth embodiment with referenceto FIGS. 8 and 9. As illustrated in FIG. 8, a protection circuit 41 ofthe fourth embodiment is provided with both the threshold signalgenerating circuit 6 of the first embodiment and the voltage change ratedetection circuit 32 of the third embodiment and a comparator CP2 isdisposed in the voltage change rate detection circuit 32 side. Theoutput signals Vcmp1 and Vcmp2 of the comparators CP1 and CP2 are eachinputted to a logic circuit LC3.

Next, a description will be given on the operation of the fourthembodiment with reference to FIG. 9. It is assumed that the thresholdsignal generating circuit 6 side is the protection circuit portion 41(1)and the voltage change rate detection circuit 32 side is the protectioncircuit 41(2). FIG. 9 illustrates the range of voltage elevation speedwhich can be responded by each of the protection circuit portions 41(1)and 41(2). When an overvoltage occurs, the protection circuit portion41(1) compares the threshold signal Vth1 and detection signal Vdet andoutputs the overvoltage detection signal Vcmp1 as described in the firstembodiment. The protection circuit portion 41(2) compares the thresholdsignal Vth2 and the voltage change rate signal Vdiff and outputs theovervoltage detection signal Vcmp2 as described in the third embodiment.

For example, when the logic circuit LC3 is configured by an OR gate, itis possible to choose which circuit to respond with depending upon thevoltage elevation rate as illustrated in FIG. 9. When the voltageelevation ate is large, the protection operation may be performed by theprotection circuit portion 41(2) which is advantageous in terms ofresponse speed. When the voltage elevation rate is small, the protectionoperation may be performed by the protection circuit portion 41(1) whichis noise tolerant.

According to the protection circuit 31 of the third embodiment, theprotection operation can be performed at higher speed compared to thefirst embodiment. However, in devices such as power electric devicesthat handle large electric power and therefore have high noise level,the protection circuit 31 may malfunction by the surge voltage generatedat the time of switching. Thus, by employing the configuration of thefourth embodiment, it is possible to secure reliability even under anenvironment with high noise level. Further, in the configuration of thefourth embodiment, it is possible to improve the noise tolerance of theprotection circuit portion 41(2) by increasing the threshold Vth2 of thedifferentiation circuit, thereby allowing the detection accuracy to beimproved as well.

Fifth Embodiment

Next, a description will be given on a fifth embodiment with referenceto FIGS. 10 to 13. As illustrated in FIG. 10, a protection circuit 51 ofthe fifth embodiment is provided with the addition circuit 15 of thefirst embodiment and the output signals of the voltage detection circuit5 and the addition circuit 15 are inputted to a signal delay comparator52 As illustrated in FIG. 11, the signal delay comparator 52 isconfigured by A/D converters AD1 and AD2, a delay time generator 53 thatdelays the output signal of AD1 for a certain time period, and a signalcomparator 54 that compares the output signals of the delay timegenerator 53 and AD2 and generates an output signal based on the voltageelevation rates of the signals being compared.

Next, a description will be given on the method of detecting anovervoltage. The detection signal Vdet outputted from the voltagedetection circuit 5 is inputted to the addition circuit 15 as in thefirst embodiment, arid a voltage Vplus generated which is a sum of Vdetand a certain amount of voltage Vadd. AD1 takes Vplus as an input signaland generates a discretized voltage signal VAD1. Similarly, AD2 takesVdet as an input signal and generates VAD2. Further, the delay timegenerator 53 takes VAD1 as an input signal and generates a thresholdsignal Vth3 which is delayed for a certain time period such as severalis. Vth3 and VAD2 are inputted to the signal comparator 54 andovervoltage detection signal V0V7 is outputted when VAD2 exceeds Vth3.

By employing the above described configuration, it is possible togenerate threshold signals without using analog circuitry to allowcertain amount of delay time to be added without having to considervariation of element constants and temperature properties and therebyallow stable protection threshold values to be specified.

Other Embodiments

Both of the switching elements SW1 and SW2 may be turned OFF as aprotection operation.

In the fourth embodiment, the overvoltage detection results of theprotection circuit portions 41(1) and 41(2) may be used simultaneouslyto output the overvoltage judging signal. In such case, more preciseovervoltage detection can be performed while maintaining the speedinessof the detection.

In the fifth embodiment, an effect which is the same as adding delaytime to the threshold signal can be obtained without using the delaytime generator 19 by comparing signals VAD1 and VAD2 having differentacquisition timings as illustrated in FIG. 14.

Average values may be used for the output signals VAD1 and VAD2 of theA/D converter in the fifth embodiment. In such case, the influence ofinstantaneous changes in Vdet caused by voltage ripples andelectromagnetic noise can be reduced.

The switching unit is not limited to a configuration in which twosemiconductor switching elements are series connected. It is sufficientto provide at least one switching element.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

As described above, the power converter of the embodiments may beapplied to a configuration in which a protection operation is performedto stop the switching operation when a steep elevation of direct currentpower supply voltage has been detected.

1. A power converter connected between a direct current power supply anda load, the power converter comprising: a switching unit protectioncircuit including: a switching unit energizing the load based on aninputted control signal, a voltage detector detecting a voltage of thedirect current power supply, and a protection operation portiondetecting a steep elevation of the voltage and performing a protectionoperation to stop a switching operation of the switching unit, whereinthe protection operation portion includes an addition circuit adding apredetermined voltage to the voltage detected by the voltage detectorand an integration circuit connected to an output of the additioncircuit, and wherein the protection operation is performed when adifference between the voltage detected by the voltage detector and anoutput voltage of the integration circuit reaches a certain value. 2.The power converter according to claim 1, wherein the protectionoperation portion includes a comparator comparing the voltage detectedby the voltage detector and the output voltage of the integrationcircuit.
 3. A power converter connected between a direct current powersupply and a load, the power converter comprising: a switching unitprotection circuit including: a switching unit energizing the load baredon an inputted control signal, a voltage detector detecting a voltage ofthe direct current power supply, and a protection operation portiondetecting a steep elevation of the voltage and performing protectionoperation to stop a switching operation of the switching unit, whereinthe protection operation portion includes a differentiation circuitdifferentiating the voltage detected by the voltage detector, andwherein the protection operation is performed when an output voltage ofthe differentiation circuit reaches a certain value.
 4. A powerconverter connected between a direct current power supply and a load,the power converter comprising: a switching unit energizing the loadbased on an inputted control signal, a voltage detector detecting avoltage of the direct current power supply, and a protection operationportion detecting a steep elevation of the voltage and performingprotection operation to stop a switching operation of the switchingunit, wherein the protection operation portion includes an additioncircuit adding a predetermined voltage to the voltage detected by thevoltage detector and a delay time generator connected to an output ofthe addition circuit, and wherein the protection operation is performedwhen a difference between the voltage detected by the voltage detectorand an output voltage of the delay time generator reaches a certainvalue.
 5. The power converter according to claim 1, wherein theswitching unit is configured by two semiconductor switching elementsparallelly connected to the direct current power supply, and wherein theprotection operation portion causes the switching unit short circuit theload as the protection operation.
 6. The power converter according toclaim 2, wherein the switching unit is configured by two semiconductorswitching elements parallelly connected to the direct current powersupply, and wherein the protection operation portion causes theswitching unit to short circuit the load as the protection operation. 7.The power converter according to claim 3, wherein the switching unit isconfigured by two semiconductor switching elements parallelly connectedto the direct current power supply, and wherein the protection operationportion causes the switching unit to short circuit the load as theprotection operation.
 8. The power converter according to claim 4,wherein the switching unit is configured by two semiconductor switchingelements parallelly connected to the direct current power supply, andwherein the protection operation portion causes the switching unit toshort circuit the load as the protection operation.
 9. The powerconverter according to claim 1, wherein the protection operation portionincludes a logic operator generating drive signal of the switching unitby performing a logical operation of the control signal and a triggersignal generated for performing the protection operation, and whereinthe logic operator performs the protection operation with priority overthe control signal.
 10. The power converter according to claim 2,wherein the protection operation portion includes a logic operatorgenerating a drive signal of the switching unit by performing a logicaloperation of the control signal and a trigger signal generated forperforming the protection operation, and wherein the logic operatorperforms the protection operation with priority over the control signal.11. The power converter according to claim 3, wherein the protectionoperation portion includes a logic operator generating a drive signal ofthe switching unit by performing a logical operation of the controlsignal and a trigger signal generated for performing the protectionoperation, and wherein the logic operator performs the protectionoperation with priority over the control signal.
 12. The power converteraccording to claim 4, wherein the protection operation portion includesa logic operator generating a drive signal of the switching unit byperforming a logical operation of the control signal and a triggersignal generated for performing the protection operation, and whereinthe logic operator performs the protection operation with priority overthe control signal.
 13. The power converter according to claim 5,wherein the protection operation portion includes a logic operatorgenerating a drive signal of the switching unit by performing a logicaloperation of the control signal and a trigger signal generated forperforming the protection operation, and wherein the logic operatorperforms the protection operation with priority over the control signal.14. The power converter according to claim 6, wherein the protectionoperation portion includes a logic operator generating a drive signal ofthe switching unit by performing a logical operation of the controlsignal and a trigger signal generated for performing the protectionoperation, and wherein the logic operator performs the protectionoperation with priority over the control signal.
 15. The power converteraccording to claim 7, wherein the protection operation portion includesa logic operator generating a drive signal of the switching unit byperforming a logical operation of the control signal and a triggersignal generated for performing the protection operation, and whereinthe logic operator performs the protection operation with priority overthe control signal.
 16. The power converter according to claim 8,wherein the protection operation portion includes a logic operatorgenerating drive signal of the switching unit by performing a logicaloperation of the control signal and a trigger signal generated forperforming the protection operation, and wherein the logic operatorperforms he protection operation with priority over the control signal.